Electron beam exposure apparatuses include a point-beam type apparatus which uses a beam spot and a variable rectangular beam type apparatus which uses a beam having a variable-size rectangular cross section.
A point-beam type electron beam exposure apparatus uses a single electron beam and can perform drawing at high resolution. However, the electron beam exposure apparatus has a low throughput and thus is only used in limited applications such as research and development, exposure mask manufacturing, and the like. A variable rectangular beam type electron beam exposure apparatus has a throughput which is one or two orders of magnitude higher than that of a point-beam type apparatus. Since the electron beam exposure apparatus basically uses a single electron beam for drawing, it often has a problem with the throughput in exposing a pattern comprising highly-integrated fine patterns of about 0.1 μm.
To solve this problem, there is available a stencil mask type electron beam exposure apparatus. The apparatus forms a pattern to be drawn in a stencil mask as pattern-transmitting holes and transfers the pattern to be drawn onto a sample surface through a reduction electron optical system by illuminating the stencil mask with an electron beam. Japanese Patent Laid-Open No. 9-245708 discloses a multi electron beam exposure apparatus. The apparatus illuminates a substrate having a plurality of apertures with electron beams, irradiates a sample surface with a plurality of electron beams having passed through the plurality of apertures through a reduction electron optical system, and deflects the plurality of electron beams to scan the sample surface. At the same time, the apparatus draws a desired pattern by individually applying/not applying the plurality of electron beams in accordance with a pattern to be drawn. In both apparatuses, an area to be exposed at one time, i.e., exposure area is larger than a conventional apparatus. Accordingly, the throughput can be increased.
However, since the area to be exposed at one time, i.e., exposure area is larger than the conventional apparatus, use of an astigmatism correcting unit arranged in a reduction electron optical system for correcting astigmatism of the reduction electron optical system causes an aberration other than astigmatism (particularly, distortion). It is thus difficult to form a desired pattern on a wafer.
Japanese Patent Laid-Open No. 9-245708 also discloses an electron beam exposure method of performing drawing while scanning a wafer with electron beams. FIG. 8A shows a conventional scanning electron beam exposure apparatus. In FIG. 8A, reference symbol S denotes an electron source which emits an electron beam, and B, a blanker. An electron beam from the electron source S forms an image of the electron source S at the same position as the blanker B through an electron lens L1. The image of the electron source is reduced and projected onto a wafer W through a reduction electron optical system comprising electron lenses L2 and L3. The blanker B is an electrostatic deflector which is located at the same position as the image of the electron source S formed through the electron lens L1. The blanker B controls whether to irradiate the wafer with an electron beam. More specifically, when the wafer is not to be exposed to an electron beam, the blanker B deflects the electron beam, and a blanking aperture BA located on the pupil of the reduction electron optical system cuts off the deflected electron beam, i.e., an electron beam EBoff. On the other hand, when the wafer is to be exposed to an electron beam, an electron beam EBon having passed through the blanking aperture BA is controlled by an electrostatic deflector DEF to scan the wafer W.
A method of performing drawing on the wafer by scanning will be described with reference to FIG. 8B. For example, to draw a pattern of a character “A”, a drawing region is divided into a plurality of pixels. While the deflector DEF moves an electron beam to perform scanning in the X direction, the blanker B performs control such that each pixel constituting part of the pattern (gray portion) is irradiated with the electron beam and each of the remaining pixels shields the electron beam. When the scanning in the X direction ends, the electron beam is stepped in the Y direction, and the scanning in the X direction restarts. Electron beam irradiation is controlled during the scanning, thereby drawing the pattern.
However, when pixels are exposed by scanning with an electron beam, the position of the electron beam in the scanning direction (X direction) changes over time while the position of the electron beam in a direction perpendicular to the scanning direction (Y direction) remains constant, as shown in FIG. 9A. The pixel exposure distribution in the scanning direction (X direction) has the average value or integrated value obtained when the electron beam moves between the pixels (to be referred to as a moving average hereinafter), as shown in FIG. 9B. FIG. 9C shows the resulting pixel intensity distribution (moving average). In this case, even if an electron beam has an axisymmetric Gaussian intensity distribution, drawing by scanning causes the intensity distribution to spread in the scanning direction (X direction). The intensity distribution looks as if there were astigmatism. Thus, it is difficult to form a desired fine pattern on a wafer.